1. Field of the Invention
The present invention relates to a method for repairing a liquid crystal panel and, more particularly, to a method for repairing a defective cell of a liquid crystal panel.
2. Description of the Related Art
Recently, a liquid crystal display (LCD) receives much attention as a next-generation advanced display device which has low power consumption, has good portability, is technology-intensive, and has high added value.
In general, in order to use liquid crystal for a display, liquid crystal cells should be formed. The liquid crystal cells are formed by filling liquid crystal between two glass substrates or between transparent plastic substrates.
In order to apply a voltage to the liquid crystal, transparent electrodes (common electrode and pixel electrode) are formed on the substrates, and the transparent electrodes serve to control an ON/OFF operation by applying the voltage to the liquid crystal.
Namely, light transmittance of the LCD is controlled by the voltage applied to the transparent electrode, and characters/images are displayed according to a light shutter effect.
Among the LCDs, an active matrix type LCD having switching elements for controlling ON/OFF operations of voltage by pixels is spotlighted with its high resolution and good video implementation capabilities.
The active matrix type LCD includes a liquid crystal panel in which liquid crystal cells are arranged in a matrix form and driving circuits for driving the liquid crystal panel.
The LCD is divided into a TN (Twisted Nematic) mode LCD using vertical fields and an IPS (In-Plane Switching) mode LCD using in-plane fields according to the field direction.
Here, the TN mode LCD, in which liquid crystal is driven by vertical fields between pixel electrodes and common electrodes disposed in a facing manner on the upper substrate, is advantageous in that it has a large aperture ratio, but disadvantageous in that its viewing angle is narrow.
The IPS mode LCD, in which liquid crystal is driven by in-plane fields between the pixel electrodes and the common electrodes disposed in parallel on the lower substrate, is advantageous in that its viewing angle is wide but disadvantageous in that it has a small aperture ratio.
The related art method for repairing a defective cell based on the structure of the TN mode LCD, among the several modes of LCDs, will now be described with reference to FIG. 1.
FIG. 1 is a sectional view of the LCD used for explaining the method for repairing a defective cell of the LCD according to the related art.
A liquid crystal panel 10 of the related art LCD includes an upper array substrate 21 (i.e., a color filter array substrate) comprised of black matrixes 23, color filters 25a, 25b and 25c, an overcoat layer 27, a common electrode 29, and a upper alignment layer (not shown) sequentially formed thereon; a lower array substrate 11 comprised of TFTs 15, pixel electrodes (not shown) and a lower alignment layer (not shown) formed thereon; and liquid crystal 41 injected in an inner space between the upper array substrate 21 and the lower array substrate 11.
Here, the black matrixes 23 are formed on the upper array substrate 21 such that they correspond the TFT region and regions of gate lines and data lines of the lower array substrate 11, and prepare cell regions where the color filters 25a, 25b and 25c are formed.
Further, the black matrixes 23 prevent a light leakage and enhance the contrast by absorbing external light, and the color filters 25a, 25b and 25c are formed at the cell region separated by the black matrixes 23 and on the black matrixes 23.
The color filters 25a, 25b and 25c are formed by R, G and B to implement R, G and B colors, and a common voltage is supplied to the common electrode 29 to control the arrangement of liquid crystals. A spacer (not shown) serves to maintain a cell gap between the upper array substrates 21 and the lower array substrate 11.
Although not shown, each TFT 15 includes a gate electrode formed with a gate line (not shown) on the lower substrate 11, a semiconductor layer (not shown) overlapping with a gate insulating layer (not shown) formed on the gate electrode (not shown), and source and drain electrodes (not shown) formed with a data line (not shown) on the semiconductor (not shown).
The TFT 15 supplies a pixel signal from the date line to a pixel electrode (not shown) in response to a scan signal from the gate line. The pixel electrode (not shown) made of a transparent conductive material with high light transmittance contacts with the drain electrode (not shown) of the TFT with a passivation layer (not shown) interposed therebetween. The upper and lower alignment layers (not shown) for liquid crystal alignment are formed by coating an alignment material and then rubbing it.
To inspect the related art liquid crystal panel with such a structure, a test pattern (not shown) is run on a screen of the liquid crystal panel 10 and it is checked whether or not there is a defective pixel. If a defective pixel is discovered, a repairing operation is performed.
In this case, the defects of the liquid crystal panel 10 includes a color deficiency of each pixel cell, point defects such as bright spots (i.e., a cell which is always turned on), dark spots (blind spots) (a cell which is always turned off), line defects caused by shorts between the gate wirings (not shown) and the data wirings (not shown), and the like.
The defects are clearly seen to an operator (worker) when the test patterns are displayed on the liquid crystal panel 10, and the operator recognizes positions of defective pixels and perform repairing thereon.
Although not shown, when a black pattern is run on the screen, a darkening (blackening, or making dark spots) process is performed to repairing defective cells appearing as bright spots because of a short deficiency, signal deficiency, etc.
In the related art, in order to repair bright spots, a method in which a pixel electrode of a defective cell is welded by laser to the gate wiring, and a portion of the pixel electrode is cut to make a gate voltage applied to the gate wiring remain at the defective cell, is typically used.
Meanwhile, if a thin film of the upper or lower array substrates is defective, repairing is performed by using rework or laser, and in this case, if there is a foreign material (D) between thin films of the upper and lower array substrates to generate a defective cell, repairing by rework or laser is not easy.
With such a foreign material, the upper alignment layer positioned to correspond to the foreign material is not uniformly rubbed during a rubbing process, resulting in a non-uniform alignment region in the liquid crystal panel.
Then, a light leakage occurs at the non-uniform alignment region in the liquid crystal panel, which deteriorates light transmittance of liquid crystal to cause bright spots to appear on the liquid crystal panel.